Electroless plating of a substrate with nickel-iron alloys and the coated substrate



ELECTROLESS PLATING OF A SUBSTRATE WITH NICKEL-IRON June 7, A. F. SCHMECKENBECHER ALLOYS AND THE COATED SUBSTRATE Filed Dec. 28, 1961 2 Sheets-Sheet 1 2.5 AMPS 26 (is ILICONE OIL 28 2.5 AMPS ofimmmc FIELD 1s OERSTEDS FIG. 1

PLURALITY OFZgLASS CYLINDERS FIG. 3

PLURALITY 0F GLASS CYLINDERS 20 INVENTDR ARNOLD F. SCHMECKENBECHER ZNDELECTROLESS SOLUTION 25.

ATTORNEY June 7, 1966 A. F. SCHME-CKENBECHER 3, 5,033

ELECTROLESS PLATING OF A SUBSTRATE WITH NICKEL-IRON ALLOYS AND THE COATED SUBSTRATE Filed D90. 28, 1961 2 Sheets-Sheer. 2

e F N '2 3 RATIO Ni Fe" IN ELEOTROLESS PLATING SOLUTION I I l l l 1 1 1 I THICKNESS T000 COAT *2 INT FIG. 6

DEPOSITION TIME (BOTH COATS) FIG. 8

JL 25N SEC 900 1200 1500 H OERSTED (500MA/INCH) GAUSS .4 LINES /INCH United States Patent 3 255 033 ELECTROLESS PLATniiG or A SUBSTRATE WITH NlCKEL-IRGN ALLOYS AND THE COATED SUB- STRATE Arnold F. Schmeckenbecher, Poughkeepsie, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 28, 1961, Ser. No. 162,894 4 Claims. (Cl. 117-47) This invention relates to electroless chemical deposition of magnetic material on coated non-metallic substances and more particularly to the deposition of nickel iron alloys on activated glass, ceramic or plastic substrates.

An object of the invention is the provision of chemical materials and processes whereby useful films of magnetic materials may be rapidly deposited directly upon metallic films or substrates Without the need for preliminary sensitizing of the underlying metal.

Another object of the invention is the provision of electroless chemical deposit processes for establishing adherent ferro-magnetic thin films upon undercoatings or metal substrates without the need for preliminary treatment with stannous or palladous sensitizing or separate chelating treatments as required in the prior art.

Another object of the invention is the provision of electroless magnetic film deposition processes for establishing oriented anisotropic magnetic films as adherent outer coatings rich in percentage of nickel and deposited quickly and directly with the employment of moderate heating conditions, 4

Another object of the invention is the provision of improved alkaline nickel iron chemical deposit baths into which chelating agents are added and also agents to induce controlled decompositions.

Another object of the invention is the provision of better electroless chemical compositions and methods of utilizing sodium hypophosphite as a reducing agent in a nickel iron bath wherein the metal salts are proportioned to result in a deposit high in nickel and exceptionally low in the percentage of phosphorous found in the resulting thin magnetic film.

Another object of the invention is the provision of an electroless chemical deposit method for producing an oriented anisotropic thin magnetic film by the combined effect of an oriented undercoat and an additional magnetic field present during the submersion of the substrate in the ferromagnetic solution. In the case of depositing magnetic material on a precoated cylindrical glass rod, a wire is situated through the center of the rod and carries current to create a magnetic field coincident with the orientation of the undercoat and serving to further orient the chemical deposition of an additional magnetic alloy on the cylindrical surface of the glass. As a combined coating, the thicknesses of both layers may be about 8000 A.

Another object of the invention is the economical production of electroless nickel iron coatings on glass, ceramic or plastic rods or sheets for use as bistable elements in computer memory or logic devices. It was found that by use of the disclosed process magnetic elements were created which had several desirable magnetic characteristics of good squareness ratio and coercive force making them easier and faster to switch from one stable state to the other and thus requiring cheaper driving elements as well as being cheaper to manufacture per se.

The present method of creating magnetic storage elements electrolessly does away with many of the troubles heretofore associated with the vacuum deposition and electroplating methods of depositing magnetic materials on substrates. These other methods are expensive and difiicult to perform, diflicult to maintain uniform film thickness throughout and limited as to production batches by the size of available vacuum chambers and electroplating holders. Here by simple and inexpensive chemical deposition processes one or more magnetic material coatings or films may be added merely by dipping into large containers with large numbers of parts treated all at the same time.

Another object of'the invention is the provision of a chemical coating process for'deposition of a nickel iron alloy from an electroless bath wherein the proportion of iron in the solution may be maintained low proportionately because the chemical bath is coated with a layer of silicone oil or otheroxidation preventing barrier.

Another object of theinvention is the production of an effective outer metallic anisotropic layer'on a foundation of metal or on a substrate which is previously coated by any ordinary deposition method or in a special way as set forth in my copending case noted hereinafter. In-the case of a plurality of layers of magnetic deposits, it was found that the special outside film or layer contributed to the production of an economical form of magnetic memory element having a high ratio of remanence to saturation induction (excellent rectangular hysteresis characteristics) a low coercive force, a lowswitching constant, high value of resistivity, a fast response time and no disturbed sensitivity,

A further object of the invention is to provide a method of creating a magnetic storage element in the form of a flat or toroidal thin film which method comprises the steps of depositing a plurality of layers of nickel iron alloys from a succession of baths containing hypophosphite by chemical means onto a substrate. The ratio of nickel to iron in the composite film is proportioned to be close to 4 to 1 preferably 79 to 21, with iron preferably higher in the undercoat and nickel present to a greater degree in the outer coat and the presence of phosphorous minimized to less than 1%.

A further object of the invention is to provide an improved electroless magnetic outer coating on a metallic undercoat. More specifically, it deals with a method of using a heated solution of nickel iron comparatively rich in nickel ions as an oriented adherent overcoat film on a previously deposited undercoat of thin magnetic film which is caused to adhere to plastic or glass by containing a high percentage of iron and other chelating factors.

Although herein the emphasis is on magnetic material outer coatings for use with magnetic memory elements, it is to be understood that other uses are contemplated. Since the various composite coatings are of good adherence to glass, ceramic and plastic substrates, the coatings and films are useful in a preliminary way for thicker deposits and added coatings in general. The outer coating is in itself of such good magnetic qualities that it may be placed upon active surfaces in general and not only on the film of the particular example set forth herein.

The present application relates mainly to means for forming outer films, layers or overcoatings of ferromagnetic material upon other metallic layers or substrates. It also discloses methods and compositions for forming undercoatings which cooperate very well, especially for magnetic effects, with the outer magnetic films or overcoats of this case. The claims for the means for forming preliminary layers or underlying films and multiple or composite films are set forth in my copending-patent application Serial No. 162,897 filed on December 28, 1961, and now abandoned.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.

3 In the drawings: FIG. 1 is an elevation view showing the apparatus for depositing a preliminary film or a complete anisotropic ferromagnetic coating.

FIG. 2 is an elevation view showing the apparatus for depositing a secondary film or coating.

FIG. 3 is an elevation view showing in schematic fashion one way in which a plurality of substrates such as glass cylinders may be coated with the preliminary film similar to the one *deposited in FIG. 1.

FIG. 4' is an elevationview showing the' apparatus by which a plurality of cylinders may receive a secondary coating in a fashion somewhat similar to that set forth with respect to a single cylinder in FIG. 2.

FIG. 5 is a chart showing the proportions of Nickel/ Iron in thin film as deposited electrolessly by various proportions of Ni++/Fe++ in solution. The one curve represents proportions when the solution is exposed to air and the other curve represents proportions when the solution is covered to prevent oxidation.

FIG. 6 is a chart showing how deposition thickness varies with deposition time with respect to the two different ferromagnetic films, one superimposed upon the other.

FIG. 7 is a chart showing S curves depicting the magnetic characteristics, with the coercive force projected to depict corresponding induced magnetic flux. The two 'curves' are representative of magnetic conditions created by impulses of different duration.' The one being a comparatively long impulse of 500 N seconds and the other produced by spike pulse of 25 N seconds.

FIG. 8 shows a rectangular hysteresis curve generated by magnetic switching of a magnetic storage element made by the chemical deposition methods set forth herein; said element then being operated in the easy anisotropic direction.

Since the advent of use of magnetic elements for storage and memory purposes, there have been proposed many materials and processes involving sintered compositions, and electroplated or evaporated films. The present instance is a departure therefrom in the use of electroless chemical deposition processes for coating memory elements with magnetic materials. Although in a general way, ferrous hypophosphite chemical coating baths are not new, the particular formulations disclosed here yield new qualities of fine adherence on smooth substrates, low content of non-metallics in the deposited film, film rich in magnetic constituents of nickel and iron, and excellent magnetic characteristics.

Heretofore, conventional electroless metal films should have been classified as metal-phosphide films with a range of phosphorous content up to 20%. Now the films disclosed here contain less than 1% phosphorous (often less than 0.25%) which is comparable to the range of so-called impurities found in nickel-iron films plated by the expensive processes of electrodeposition or vacuum deposition. These new metal rich qualities aid for adherence of the 80/20 NiFe type film, its rapid deposition and its good magnetic qualities. There is disclosed here a method of creating a magnetic storage device in a flat or toroidal thin film, which method comprises the step of depositing one or more layers of nickel-iron alloys containing phosphorous by chemical means onto a substrate, the ratio of nickel to iron in the created film proportioned to be close to or at 80/ 20, with iron preferably higher in the under- .coat and nickel 'higher in the outer coat, with the presence of phosphorous minimized to less than 1% phosphorous. Overall film thickness may range from 6000 to 8000 A. vwith the undercoat sometimes as thick as 1000 A., but one good proportion is a 100 A. undercoat covered with a 7000 A. outer layer which is achieved by a two minute dip into the first solution for the undercoat followed by an eight minute dip into the second solution for the outer coat. Although the plastic or ceramic substrate surface is isotropic, the layers of the film are made anisotropic because the coats are laid in the presence of a magnetic field induced for example by a current carrying Wire threaded through the center of a glass cylinder receiving the electroless films. The earths field may be taken into consideration by arranging the wire and cylinder lengthwise east to west. As an optional arrangement, permanent magnets may be used to create the magnetic fields with the absence of extra heating effects. Separate storage units may be made by masking the substrate during deposition, or an entire sheet, cylinder or other shape may be coated and then cut into smaller sections.

Turning now to the drawings, it may be explained that FIG. 1 shows a single glass cylinder 20. which is dipped into a first chemical bath 21 at room temperature for a period of two minutes during which time an orienting field is established by electrical current in the Wire 22. Thus a preliminary film or undercoating 23 is deposited on the surface of the cylinder 20.

After the cylinder 20 is taken out of the first solution 21, it is allowed to dry and then is dipped into a second solution 25 shown in FIG. 2. In FIG. 2 the flask 26 is suspended in hot water held in a separate container 27 which is maintained at such a temperature so that the solution 25 is maintained at about 75 C. After cylinder 20 is plunged into the solution 25, the solution is immediately coated with the layer of silicone oil 28 which is added to prevent oxidation of the constituents of the solution and mainly to prevent the Fe ions from changing from Fe++ During this same second coating operation to Fe+++. which is to last about eight minutes, the wire 22 carries a current of about 2.5 a. to create a field of about 13 oersteds to orient the deposit as it is' formed around the cylinder. The second coating 29 thus formed is deposited directly on the preliminary magnetic coating and although the undercoating is only about A., the second coating is quite a bit thicker to the point of 8000 A.

FIGS. 3 and 4 are quite a bit similar to the apparatus of FIGS. 1 and 2, respectively, the only difference being that arrangements are made for coating a plurality of cylinders 20 at the same time. In FIG. 3 the series of elongated glass cylinders 20 are shown mounted on two end pieces 31 in a circular array with space between the cylinders allowing free deposition action to take place. The first solution 21 is held in a container 32 and the entire array of cylinders 20 is submerged in the solution. This is also maintained at room temperature and a continuous wire 33 is employed to carry current through all the cylinders so that an orienting magnetic field is created around the surface of all cylinders to control the anisotropic character of the deposited undercoating.

After the required time of submersion, for example, two minutes, the assembly of cylinders is removed and allowed to dry before the submersion in the second solution 25 shown in the apparatus of FIG. 4. There it is seen that an enlarged holder 35 contains hot water which maintains the second solution at about 75 C. Mounted inside container 35 is a secondary container 36 with walls which extend above the water level mark of container 35 and formed with a hinged lid 37 which may be raised to allow insertion of the array of cylinders 20 and also the addition of a layer 28 of silicone oil to limit or eliminate oxidation. In this secondary coating operation, the orienting field is again created through wire 33 and the deposition process is allowed to continue for about eight minutes.

Before explaining how the coatings are varied as to nickel-iron content and thickness as shown in the charts, it is believed best to set forth first the actual constituents of the two solutions or baths and the various examples of such which have been found very effective. The open ends of cylinder 20 may or may not be plugged depending whether or not an interior film is desired.

It has been found that uniform, well adhering nickel-.

iron films may be deposited on non-metallic surfaces, such as glass, plastics, etc., at temperatures from 0 C. to 99 0., preferably at room temperature, by inducing con;

trolled decomposition of the plating solution and interrupting the plating after a desired thickness of the metal film has been deposited. The films adhere particularly well to the glass if they contain a comparatively high percentage of iron.

The plating solution 21, FIG. 1, contains several components; a nickel salt (.5 g. Ni/liter or more), a ferrous salt (.5 g. Fe/liter or more), hypophosphite ions and a sequestering agent, dissolved in water. In addition, however, a small amount of ions of palladium is added to the acid plating solution at room temperature. The hypophosphite ions reduce the noble metal ions to the metal without setting free hydrogen. The metal is distributed as small particles of colloidal dimensions in the solution. The solution is now made alkaline by adding ammonia, triethanolamine or the like, and the smooth surface to be plated is immediately brought into contact with the solution.

If the surface to be plated is glass, such as cylinder 20, FIG. 1, the adhesion of the film 23 is improved if the glass has been soaked with sodium hydroxide solution or another strong alkaline solution for thirty minutesor more, or with diluted hydrogen fluoride or ammonium fluoride solution before plating.

It is not necessary to activate the surface to be plated by rinsing with stannous chloride and subsequently with palladium chloride before plating.

After immersion of the glass cylinder 20 and within a few minutes, hydrogen gas is set free and a clear uniform Well adhering nickel-iron film 23 is depositedon all exposed surfaces.

For the first example of the 1st electroless solution21 to form a preliminary coating 23, the following formulation and process may be noted:

EXAMPLE 1 Grams Sodium hypophosphite .5 Sodium potassium tartrate 1.5 Ferrous ammonium sulfate 1.0 Nickelous sulfate .7

were dissolved in 20 ml. water.

A few drops of diluted sulfuric acid were added to bring the pH value of the solution to about 4.0.

.5 ml. of a 0.1% solution of palladium chloride in water containing 0.1% conc. hydrochloric acid, were added.

After one minute, 3.5 ml. of 29% ammonium hydroxide were added to bring the pH value of the solution to 9.2.

ml. of the solution were placed into a test tube 24 into which a .glass surface is brought after being previously treated with 10 N NaOH for thirty minutes at room temperature, separated and the glass thoroughly rinsed with distilled water.

After thirty minutes the glass is taken out ofbath 21, rinsed with water, then with acetone and dried.

The metal film 23 formed on the glass was clear, continuous and adhered well. It was about 1000 A. thick, contained 70% Ni, 30% Fe, was ferromagnetic and had a coercive force of about 10 oersteds.

As a 2nd example of the 1st electroless solution used to form a preliminary coating 23, the following formulation and process may be noted:

EXAMPLE 2 Grams Sodium hypophosphite .5 Sodium potassium tartrate 1.5 Nickelous chloride .2 Ferrous chloride 1.5

were dissolved in 20 ml. water.

A few drops of hydrochloric acid were added to bring the pH value of the solution to about 4.0.

.5 ml. of'a 0.1% solution of palladium chloride in water containing 0.1% hydrochloric acid were added.

After about one minute, 3.5 ml. of 29% ammonium hydroxide were added to bring the pH value of the solution to about 9.2.

10 ml. of the solution were filled into test tube 24 and a glass surface 20 presented thereto, said glass surface 20 being previously treated with a 1% solution of ammonium fluoride in water and left standing at room temperature for thirty minutes, then separated and the glass 20 thoroughly rinsed with distilled water.

After tenminutes of plating the glass surface 20, the glass was separated and rinsedwith Water. Nickel-iron films with good magnetic properties and containing 50% or more of nickel, can be depositedon-an'underlayer,

the deposition of which is described above, as an example. However, they also may be deposited on non-metallic surfaces.- activated by the conventional stannou-s chloride and palladium chloride rinses, or on non-metallic or metallic surfaces activated by other methods. A detailed description of the deposition of the nickel-iron films follows. The process is somewhat like the deposition of the underlayer already described with the exception of afew essential details. A second 10 ml. of a second electroless plating bath25 was placed into the second test tube 26.

This second bath was used to deposit an overcoating 29 upon the undercoating 23 producedby Example 2, bath 21.

As an example, thesecond plating solution contained:

Sodium hypophosphite grams .5 Sodium potassium tartrate do 1.5 Nickelous chloride do 1.0 Ferrous chloride do .5 29% ammonium hydroxide ml 7 in 20 ml. water.

The plating solution was heated at 75 C. by placing test tube 26 in a tank27 containing hot water which is maintained hot enough to insure a constant 75 C. of the solution 25.

After ten minutes anickel-iron film 29 of an average thickness of about 15,000 A. had been plated on top of the -iron;rich nickel-iron underlayer 23.

The film 29 adhered firmly to the underlayer 23, which in turn adhered to the glass .20. The combined coating was ferromagnetic and had a coercive force of about 4 oersteds.

While these electroless plating operations are taking place as described inthe foregoing and shown in FIGS. 1 and 2, the wire 22 remains threaded through cylinder 20 anda current of about 2.5 amperes is impressed therein to create an orienting field of about 13 oersteds at the surface of cylinder 20 for creating circumferential anisotropic deposits of the magnetic material. The loose end of wire 22 is held removedas far as possible from the surface coating 23 to avoid disturbing the regular orientation thereof.

In a copendingapplication, Serial No. 99,739, now Patent No. 3,183,537 filed on March 31, 1961, it is shown that separate small thin film magnetic elements may be made from larger objects such as glass cylinders which are coated in bulk. The process disclosed and claimed there relates to the technique of embedding a bundle of coated glass cylinders in a reversible cement While they are sliced or cut into toroids suitable for magnetic memory array elements.

Before explaining in greater detail the process and electroless bath formulation for the second coat 29 already noted in a general way, it may be pointed out that a process is disclosed to electrolessly plate nickel-iron films of unusual magnetic properties on metal surfaces, preferably on very thin nickel-iron films previously plated on non-metallic surfaces by the method described with.

respect to preliminary coat 23 hereinbefore. The nickeliron films 23 and 29 have a high ratio of saturation induction to remanence (squareness ratio), a low coercive force, low switching constant and other properties desirable for applications in computer memories and logic element circuits. These films contain 75-81% nickel, less than 1% phosphorus and the balance in iron.

A detailed account of bath 2 for the second coat 29 is as follows:

The film 29 is prepared by bringing the surface 20 to be plated at 75 90 C. for 330 minutes in contact with a solution which contains 20 grams/liter to 50 g./ 1., preferably 30 g./l. of NiCl -6H O or of another Ni++ -salt and an amount of Fe++ -salt, preferably FeCl -4H O, which corresponds to a ratio of Ni++ to Fe++ of 1.48 to 1.53, preferably 1.50, 50 grams/liter of 150 g./l. of

sodium potassium tartrate, g./ l. to 50 g./l. preferably 25 g./l. of radium hypophosphite or a corresponding amount of another metal hypophosphite or by hy-pophos phoric acid, and ammonia to bring the pH to 8-1-2, pref erab'ly 11.

Another resume or detailed description of the method of applying magnetic coatings is as follows:

A piece of glass tubing 20, FIG. 1, of'0.03 OD. and about 4" length is kept in a solution of 4 g. of sodium hydroxide in 10 ml. of water, for about 30 minutes after which it is taken out and rinsed with water. Alen gth of #28 copper wire 22 is passed through the tube and connected to a DC. power supply, 2.5 amps. are passed through the wire during plating.

5 grams of sodium hypophosphite, grams of Rochelle salt and 1 gram of nickelous chloride are dissolved in 200 ml. water. 10 ml. of this solution is filled into a small beaker. 1 ml. of a solution containing 0.2 g. of ferrous chloride per milliliter is added. Then 0.5 ml. of 0.1% solution of palladium chloride is added. After 30 seconds 3 ml. 'of 28% ammonium hydroxide solution is added. The mixture 21 is'transferred to a small test tube 24. The glass tube to be plated is dipped into the mixture and left in it for two minutes at room temperature. Then the'tube 20 is taken out and rinsed with water.

In preparation for the second bath, FIG. 2, 5 grams of sodium hypophosphite, 15 grams of Rochelle salt and 6 grams of nickelous chloride are dissolved in 200 ml. of water. 10 ml. of this solution is filled into a small beaker. 1.95 ml. of a solution containing 0.05 g. of ferrous chloride per liter is added. 3 ml. of 28% ammonium "hydroxide solution is added. The mixture 25, FIG. 2, is transferred into a small test tube 2 6. The test tube is put into a water bath kept at 75 C. After about half a minute, the glass tube 20 to be plated is dipped into the plating mixture. A few drops of silicone oil 28 are added to the mixture to protect the plating solution from the atmosphere. The tube to be plated is left in for eight minutes, then taken out, rinsed with water, then with acetone, dried and coated with a lacquer for protection (for instance, by dipping into an acrylic lacquer solution Kryllon). I

The graph FIG. 5 shows that the composition of the plated films depends on the composition of the plating bath. (No silicone oil used in these last mentioned procedures.) Thickness of films is controlled by the plating time, FIG. 6, temperature and composition of the plating bath.

The films plated by the described method are about 8000 A. thick, contain about-80% nickel, 20% iron and 0.5-0.25% phosphorus.

The process requires no cobalt, it is rapid, requires no heavy metal substrate and is lower in the ratios of iron and phosphorus than heretofore thought possible.

In FIG. 2 it is shown that a layer of silicone oil 28 is present on top of the second electroless solution or bath 25. This silicone layer is added directly after the cylinder 20 is placed into the bath to start deposition of the second coat. The purpose of the silicone layer is to prevent changes in the iron ions Fe++. It is found that the electroless platings are more reproducible if an is excluded from the plating solution during plating, so

the plating solution is covered with a second liquid phase of lighter specific weight than the plating solution, such as silicone oil 28. It is believed that in contact with air, a part of the Fe++ is oxidized to Fe+++, and consequently a higher concentration of Fe++ is needed in the plating solution. The ratio of Ni /Fe++ needed to plate 80% nickel, 20% iron films under exclusion of air is 2.68 to 2.73, preferably 2.70. The chart, FIG. 5 shows the proportions of Nickel/Iron in a thin film as deposited electrolessly by various proportions of Ni /Fe++ in solution. The curve A relates to a solution exposed to air, and the curve B relates to a covered solution. It is noted that'in order toattain the 80/20 nickel iron film ratio, a smaller part of iron is required in the silicone covered solution, i.e., ratio 2.7 instead of ratio 1.5 of ions in the solution. 7

FIG. 6 shows in chart form how the thickness of a composite coating of two layers is attained with respect to time of deposition. It is evident that the particular depositions referred to are those whereby two minutes are used for the first coat and eight minutes for the outer coating. FIG. 7 shows S curves of magnetic characteristics of the deposited films and vertical receptiveness or inductance of lines of flux in gauss as compared with horizontal coercivity or field strength applied in oersteds. The filmtested was the two minute plus eight minute composite film of FIG. 6. S curve C relates to a magnetic state imposed by a relatively long pulse of 500 N sec. with a low coercive force produced by 300-600 ma./inch, and in a rise. timeof about 5 N sec. S curve D relates to magnetic switching imposed by a short pulse of 25 N sec. ma./inch, and a rise time also about 5 N sec.

FIG. 8 shows hysteresis loop characteristics of composite films coated by the procedures explained relative to the other views and FIGS. 6 and 7. It is evident that the loop' has a good squareness ratio and a low coercive force which bears out the findings of fast switching speeds exhibited also in FIG. 7.

Although magnetic characteristics of thin films are a desirable attribute as stressed hereinbefore, the additional factor of adherence to high temperature substrates is also of separate value for the basic formation of electrodes and conductors for printed circuits and components in general. Therefore it is contemplated that the films noted, singly or jointly, are to be considered as applied to components in general and printed circuits with or without such components, as well as to magnetic elements v for use per se.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of plating an activated substrate comprising the steps of preparing an aqueous electroless plating bath consisting essentially of per liter of water;

30 grams of NiCl .6H O and an amount of FeCI AH O which corresponds to a ratio of Ni++ to Fe of 1.50

50 grams of sodium potassium tartrate 25 grams of sodium hypophosphite, and ammonia to bring the pH to 11, heating said bath to 75-90 (3., and inserting said activated substrate into said bath for from three to thirty minutes, whereby a magnetic memory element is formed by chemical deposition.

2. A method of plating an activated substrate comprisingthe steps of preparing an aqueous electroless plating bath consisting essentially of per liter of water;

with a coercive force produced by 600-1200 9 30 grams of NiCl .6H O and an amount of FeCI AH O which corresponds to a ratioof Ni++ to Fe++ of 2.7 e 50 grams of sodium potassium tartrate 25 grams of sodium hypophosphite plus ammonia to bring the pH to 11 plus a few drops of silicone oil to protect the plating solution from the atmosphere, heating said bath to about 75 C., and inserting said activated substrate into said bath for several minutes, whereby a magnetic memory element is formed by chemical deposition.

3. A magnetic memory element comprising an activated substrate bearing a square loop ferromagnetic film, said film being deposited by a several minute immersion in an aqueous electroless plating bath consisting essentially of per liter of water;

30 grams of NiCl .6H O and an amount of FeCl .4H O which corresponds to a ratio of Ni++ to Fe of 1.50 50 grams of sodium potassium tartrate 25 grams of sodium hypophosphite, and ammonia to bring the pH to 11, the foregoing solution to be heated to 75 90 C.

4. A magnetic memory element comprising an activated substrate bearing a square loop ferromagnetic film, 25

which corresponds to a ratio of Ni++ to Fe++ 3 of 2.7 50 grams of sodium potassium tartrate 25 grams of sodium hypophosp hite plus ammonia to bring the pH t-o 11 10 plus a few drops of silicone oil to protect the plating solution from the atmosphere and the foregoing solution to be used at about 75 C.

References Cited by the Examiner UNITED STATES PATENTS 2,827,399 3/1958 Eisenberg 106-1 2,876,116 3/1959 Jendrzynski 106-1 2,898,236 8/1959 Long et al. 117-124 2,928,757 3/1960 Lee et a1. 106-1 2,945,217 7/1960 Fisher et al. 204-43 2,976,174 3/1961 Howard 117-93.2 3,027,309 3/1962 Stephen 204-43 3,047,423 7/ 1962 Eggenberger et al. 204-43 3,051,593 8/1962 Gray et al. 117-124 3,063,850 10/1962 Mikulski 106-1 3,098,803 7/1963 Godycki et al. 204-38 3,116,159 12/1963 Fisher et al. 117-130 XR 3,119,753 1/1964 Mathias et al 204-43 3,123,484 3/1964 Pokras et al. 106-1 3,140,188 7/1964 Zirngiebl et al. 106-1 FOREIGN PATENTS 619,636 5/1961 Canada.

OTHER REFERENCES Tsu: Preparation of Adherent Thin MagnetiE' Films By Chemical Reduction, IBM Technical Disclosure Bulletin, vol. 2, No. 3, October 1959.

WILLIAM D. MARTIN, Primary Examiner.

MORRIS LIEBMAN, ALEXANDER H. BROD- MERKEL, J. E. CARLSON, J. E. CALLAGHAN, H. E. COLE, W. D. HERRICK, Assistant Examiners. 

1. A METHOD OF PLATING AN ACTIVATED SUBSTRATE COMPRISING THE STEPS OF PREPARING AN AQUEOUS ELECTROLESS PLATING BATH CONSISTING ESSENTIALLY OF PER LITER OF WATER; 30 GRAMS OF NICL2.6H2O AND AN AMOUNT OF FECL2.4H2O WHICH CORRESPONDS TO A RATIO OF NI++ TO FE++ OF 1.50 50 GRAMS OF SODIUM POTASSIUM TARTRATE 25 GRAMS OF SODIUM HYPOPHOSPHITE, AND AMMONIA TO BRING THE PH TO 11, HEATING SAID BATH TO 75*-90*C., AND INSERTING SAID ACTIVATED SUBSTRATE INTO SAID BATH FOR FROM THREE TO THIRTY MINUTES, WHEREBY A MAGNETIC MEMORY ELEMENT IS FORMED BY CHEMICAL DEPOSITION. 